I recently upgraded from 11.04 to 11.10. My machine now hangs during the shutdown process, but can reboot just fine. If I turn off quiet and splash boot options, then the following error is displayed:

Connection refusedId did not get the system bus. Make sure the message bus daemon is running!
Message: Failed to connect to socket /var/run/debus/system[fail]o

That is, the [fail] overwrites part of the error message. I am then dropped to a root shell. Running shutdown now causes the same thing to happen. Running reboot from here still succeeds.

Here's what I've tried so far:

Setting apci=off has no affect

Following the directions from this post gave FATAL: Module rt2860sta not found.

Following the directions from this post had no result, but stopped me from running reboot after being put in single-user mode; now when I do this, I get an error saying /run/lock was not mounted, a message saying the system is going to restart, and then it hangs. I can still reboot from within Ubuntu as before.

I tried all of the other ideas. I tried to work on the ACPI issues, I got rid of ModemManager, I tried all combinations of halt, etc. No dice. So I thought if a 64bit driver was messing up the shutdown, maybe a switch back to 32bit would work.

You can do an install from live disk where Ubuntu chooses to install the distro you want while retaining your documents and many of your installed programs. I did have to reinstall System Profiler, all of the DVD decrypt libraries, etc but that was not really too bad (I have a fast FIOS internet).

So for me the solution was to use 11.10 32bit. This will not be okay if you need the 64bit version. Good luck.